Blended fluoropolymer compositions

ABSTRACT

Blended fluoropolymer compositions are provided. In one embodiment, a liquid dispersion of a first fluoropolymer is blended with a liquid dispersion of a second fluoropolymer. The first fluoropolymer may be polytetrafluoroethylene (PTFE), such as a low molecular weight PTFE (LPTFE) that has been polymerized via a dispersion or emulsion polymerization process, and which has not been agglomerated, irradiated, or thermally degraded. The LPTFE may be in the form of an aqueous dispersion, having a mean particle size of less than 1.0 microns (μm), with the LPTFE having a first melt temperature (T m ) of 332° C. or less. The second fluoropolymer may be a melt processible fluoropolymer (MPF), such as perfluoromethylvinvyl ether (MFA), fluorinated ethylene propylene (FEP), or perfluoropropylvinvyl ether (PFA), for example, in the form of an aqueous dispersion, and having a mean particle size of less than 1.0 microns (μm). Blending of the dispersions facilitates interaction of the LPTFE and MPF on a submicron level to facilitate intimate blending such that, when the blended fluoropolymer composition is dried, a crystal structure representing a true alloy of the fluoropolymers is formed, having melt characteristics that differ from those of the individual fluoropolymers. The blended fluoropolymer composition may be used to provide a coating having improved impermeability, stain resistance, abrasion resistance, smoothness, and higher contact angles.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under Title 35, U.S.C. §119(e) ofU.S. Provisional Patent Application Ser. No. 61/057,597, entitledBLENDED FLUOROPOLYMER COMPOSITIONS, filed on May 30, 2008; U.S.Provisional Patent Application Ser. No. 61/100,311, entitled BLENDEDFLUOROPOLYMER COMPOSITIONS, filed on Sep. 26, 2008; U.S. ProvisionalPatent Application Ser. No. 61/145,433, entitled BLENDED FLUOROPOLYMERCOMPOSITIONS, filed on Jan. 16, 2009; and U.S. Provisional PatentApplication Ser. No. 61/145,875, entitled BLENDED FLUOROPOLYMERCOMPOSITIONS, filed on Jan. 20, 2009, the disclosures of each areexpressly incorporated by reference herein in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to fluoropolymers and, in particular,relates to blended fluoropolymer compositions having improved,synergistic properties.

2. Description of the Related Art

Fluoropolymers are long-chain polymers comprising mainly ethyleniclinear repeating units in which some or all of the hydrogen atoms arereplaced with fluorine. Examples include polytetrafluoroethylene (PTFE),perfluoromethyl vinyl ether (MFA), fluoro ethylene propylene (FEP),perfluoro alkoxy (PFA), poly(chlorotrifluoroethylene) andpoly(vinylfluoride).

Fluoropolymers are amongst the most chemically inert of all polymers andare characterized by an unusual resistance to acids, bases and solvents.They have unusually low frictional properties and have the ability towithstand extremes of temperature. Accordingly, fluoropolymers areutilised in a wide variety of applications in which resistance toextreme environments is necessary. Current applications include theformation of tubing and packing materials within chemical plants,semiconductor equipment, automotive parts and structural cladding.

SUMMARY OF THE INVENTION

The present invention provides blended fluoropolymer compositions. Inone embodiment, a liquid dispersion of a first fluoropolymer is blendedwith a liquid dispersion of a second fluoropolymer. The firstfluoropolymer may be polytetrafluoroethylene (PTFE), such as a lowmolecular weight PTFE (LPTFE) that has been polymerized via a dispersionor emulsion polymerization process, and which has not been agglomerated,irradiated, or thermally degraded. The LPTFE may be in the form of anaqueous dispersion, having a mean particle size of less than 1.0 microns(μm), with the LPTFE having a first melt temperature (T_(m)) of 332° C.or less. The second fluoropolymer may be a melt processiblefluoropolymer (MPF), such as perfluoromethylvinvyl ether (MFA),fluorinated ethylene propylene (FEP), or perfluoropropylvinvyl ether(PFA), for example, in the form of an aqueous dispersion, and having amean particle size of less than 1.0 microns. Blending of the dispersionsfacilitates interaction of the LPTFE and MPF on a submicron level tofacilitate intimate blending such that, when the blended fluoropolymercomposition is dried, a crystal structure representing a true alloy ofthe fluoropolymers is formed, having melt characteristics that differfrom those of the individual fluoropolymers. The blended fluoropolymercomposition may be used to provide a coating having improvedimpermeability, stain resistance, abrasion resistance, smoothness, andhigher contact angles.

In one form thereof, the present invention provides a blendedfluoropolymer dispersion, including polytetrafluoroethylene (PTFE)having a first melt temperature (T_(m)) of 332° C. or less, in the formof a liquid dispersion of particles having a mean particle size of 1.0microns (μm) or less; and a melt processible fluoropolymer (MPF) in theform of a liquid dispersion of particles having a mean particle size of1.0 microns (μm) or less.

In one embodiment, the polytetrafluoroethylene (PTFE) dispersion mayhave a mean particle size of 0.9 microns (μm) or less, 0.75 microns (μm)or less, 0.5 microns (μm) or less, 0.4 microns (μm) or less, 0.3 microns(μm) or less, or 0.2 microns (μm) or less, and a first melt temperature(T_(m)) of 330° C. or less, 329° C. or less, 328° C. or less, 327° C. orless, 326° C. or less, and 325° C. or less.

In one embodiment, the polytetrafluoroethylene (PTFE) dispersion isobtained via emulsion polymerization and without being subjected toagglomeration, thermal degradation, or irradiation, and includes lessthan 1.0 wt. % surfactant, based on the weight of saidpolytetrafluoroethylene (PTFE) dispersion.

In a further embodiment, the melt processible fluoropolymer (MPF) is aperfluoroalkyl vinyl ether or fluorinated ethylene propylene, and has amelt flow rate (MFR) of at least 4.0 g/10 min.

The melt processible fluoropolymer (MPF) may be perfluoropropylvinvylether (PFA), and exemplary compositions have a PFA content of 37 wt. %to 80 wt. % and a PTFE content of 20 wt. % to 63 wt. %, based on thetotal solids of the PTFE and PFA. Other exemplary compositions have aPFA content of 37 wt. % to 65 wt. % and a PTFE content of 35 wt. % to 63wt. %, based on the total solids of the PTFE and PFA. Further exemplarycompositions have a PFA content of 43 wt. % to 63 wt. % and a PTFEcontent of 37 wt. % to 57 wt. %, based on the total solids of the PTFEand PFA. Further exemplary compositions have a PFA content of 50 wt. %to 60 wt. % and a PTFE content of 40 wt. % to 50 wt. %, based on thetotal solids of the PTFE and PFA. A further exemplary compositionincludes 53 wt. % PFA and 47 wt. % LPTFE.

The melt processible fluoropolymer (MPF) may be perfluoromethylvinvylether (MFA), and exemplary compositions have a MFA content of 35 wt. %to 90 wt. % and a PTFE content of 10 wt. % to 65 wt. %, based on thetotal solids of the PTFE and MFA. Other exemplary compositions have aMFA content of 45 wt. % to 76 wt. % and a PTFE content of 24 wt. % to 65wt. %, based on the total solids of the PTFE and MFA. Further exemplarycompositions have a MFA content of 56 wt. % to 76 wt. % and a PTFEcontent of 24 wt. % to 44 wt. %, based on the total solids of the PTFEand MFA. Still further exemplary compositions have a MFA content of 63wt. % to 70 wt. % and a PTFE content of 30 wt. % to 37 wt. %, based onthe total solids of the PTFE and MFA. A further exemplary compositionincludes 67 wt. % MFA and 33 wt. % LPTFE.

The melt processible fluoropolymer (MPF) may be fluorinated ethylenepropylene (FEP), and exemplary compositions have a FEP content of 25 wt.% to 90 wt. % and a PTFE content of 10 wt. % to 75 wt. %, based on thetotal solids of the PTFE and FEP. Other exemplary compositions have aFEP content of 35 wt. % to 90 wt. % and a PTFE content of 10 wt. % to 65wt. %, based on the total solids of the PTFE and FEP. Further exemplarycompositions have a FEP content of 35 wt. % to 55 wt. % and a PTFEcontent of 45 wt. % to 65 wt. %, or a FEP content of 60 wt. % to 90 wt.% and a PTFE content of 10 wt. % to 40 wt. %, based on the total solidsof the PTFE and FEP. Still further exemplary compositions have a FEPcontent of 40 wt. % to 50 wt. % and a PTFE content of 50 wt. % to 60 wt.%, or a FEP content of 75 wt. % to 85 wt. % and a PTFE content of 15 wt.% to 25 wt. %, based on the total solids of the PTFE and FEP. Furtherexemplary compositions include either 50 wt. % FEP and 50 wt. % LPTFE,or 75 wt. % FEP and 25 wt. % LPTFE.

The present invention also provides a method of forming a blendedfluoropolymer dispersion, including the step of mixing the foregoingcomponents. A fluoropolymer powder may be obtained from the blendedfluoropolymer composition by drying the blended composition and, inparticular, freeze drying the blended composition. A coating may beformed by applying the blended fluoropolymer composition to thesubstrate, and heat curing the blended fluoropolymer composition.

In another form thereof, the present invention provides a method offorming a blended fluoropolymer composition, including the steps ofproviding a first liquid dispersion of polytetrafluoroethylene (PTFE)particles having a first melt temperature (T_(m)) of 332° C. or less anda mean particle size of 1.0 microns or less; providing a second liquiddispersion of particles of a melt processible fluoropolymer (MPF) havinga mean particle size of 1.0 microns or less; and mixing the first andsecond dispersions together.

The method may include the additional step of drying the blendedfluoropolymer composition to form a powder and, in particular, freezedrying the blended fluoropolymer composition. The method may alsoinclude the additional steps of applying the blended fluoropolymercomposition to a substrate; and heat curing the blended fluoropolymercomposition.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of this invention,and the manner of attaining them, will become more apparent and theinvention itself will be better understood by reference to the followingdescription of an embodiment of the invention taken in conjunction withthe accompanying drawings, wherein:

FIGS. 1-11 correspond to Example 1, wherein:

FIG. 1 is a chart of normalized first AH of fusion, taken from DSC data,vs. concentration of MFA;

FIG. 2 is a chart of first AH of fusion of the MFA phase, taken from DSCdata, vs. concentration of MFA;

FIG. 3 is a chart of normalized second AH of melting, taken from DSCdata, vs. concentration of MFA;

FIG. 4 is a chart of normalized second AH of melting of the MFA phase,taken from DSC data, vs. concentration of MFA;

FIG. 5 is a chart of second melt point of the MFA phase, taken from DSCdata, vs. concentration of MFA;

FIG. 6 is a chart of the AH of fusion for the MFA phase, taken from DSCdata, vs. concentration of MFA;

FIG. 7 is a chart of second melt AH for the MFA phase, taken from DSCdata, vs. concentration of MFA;

FIG. 8 is a chart of fusion temperature of the LPTFE phase, taken fromDSC data, vs. concentration of MFA;

FIG. 9 is a chart of the second melt point of the LPTFE phase, takenfrom DSC data, vs. concentration of MFA;

FIG. 10 is a chart of normalized AH of fusion for the LPTFE phase, takenfrom DSC data, vs. concentration of MFA; and

FIG. 11 is a chart of normalized second melt AH for the LPTFE phase,taken from DSC data, vs. concentration of MFA;

FIGS. 12-19 correspond to Example 2, wherein:

FIG. 12 is a chart of fusion melt point for the LPTFE phase, taken fromDSC data, vs. concentration of FEP;

FIG. 13 is a chart of second melt point for the LPTFE phase, taken fromDSC data, vs. concentration of FEP;

FIG. 14 is a chart of fusion melt point for the FEP phase, taken fromDSC data, vs. concentration of FEP;

FIG. 15 is a chart of second melt point for the FEP phase, taken fromDSC data, vs. concentration of FEP;

FIG. 16 is a chart of normalized fusion AH, taken from DSC data, vs.concentration of FEP;

FIG. 17 is a chart of normalized second melt AH, taken from DSC data,vs. concentration of FEP; and

FIG. 18 is a chart of first melt point of the FEP phase, taken from DSCdata, vs. concentration of FEP;

FIG. 19 is a chart of first melt point of the LPTFE phase, taken fromDSC data, vs. concentration of FEP;

FIGS. 20-26B correspond to Example 3, wherein:

FIG. 20 is a chart of fusion temperature, taken from DSC data, vs.concentration of PFA;

FIG. 21 is a chart of second melt point, taken from DSC data, vs.concentration of PFA;

FIG. 22 is a chart of normalized fusion AH for the PFA phase, taken fromDSC data, vs. concentration of PFA;

FIG. 23 is a chart of fusion AH for the LPTFE phase, taken from DSCdata, vs. concentration of PFA;

FIG. 24 is a chart of normalized fusion AH for the LPTFE phase, takenfrom DSC data, vs. concentration of PFA;

FIG. 25 is a chart of normalized second melt AH for the LPTFE phase,taken from DSC data, vs. concentration of PFA;

FIG. 26A is an illustration of acid etch test results of PFA/LPTFE blendfilms of Example 3; and

FIG. 26B is a chart of contact angles of water on PFA/LPTFE blend filmsof Example 3;

FIGS. 27-34 correspond to Example 4, wherein:

FIG. 27 is a chart of peak normalized second melt AH for various MPF's,taken from DSC data, vs. concentration of MPF;

FIG. 28 is a chart of peak normalized fusion AH for various MPF's, takenfrom DSC data, vs. concentration of MPF;

FIG. 29 is a chart of peak normalized LPTFE second melt AH for variousMPF's, taken from DSC data, vs. concentration of MPF;

FIG. 30 is a chart of peak normalized LPTFE fusion AH for various MPF's,taken from DSC data, vs. concentration of MPF;

FIG. 31 is a chart of LPTFE second melt point, taken from DSC data, vs.concentration of MPF;

FIG. 32 is a chart of LPTFE fusion temperature, taken from DSC data, vs.concentration of MPF;

FIG. 33 is a chart of second melt point for the MPF phase, taken fromDSC data, vs. concentration of MPF; and

FIG. 34 is a chart of fusion melt point for the MPF phase, taken fromDSC data, vs. concentration of MPF;

FIGS. 35-37 correspond to Example 5, wherein:

FIG. 35 is a DSC trace for the of MFA of Example 5;

FIG. 36 is a DSC trace for the of LPTFE of Example 5; and

FIG. 37 is a DSC trace for the of MFA/LPTFE blend of Example 5;

FIG. 38 illustrates the clamping arrangement used in Example 6;

FIGS. 39 and 40 illustrate results of the stain resistance test ofExample 7;

FIGS. 41-47 correspond to Example 8, wherein:

FIG. 41 is a chart of normalized AH of fusion of PFA vs. PFA fraction;

FIG. 42 is a chart of contact angle vs. PFA fraction;

FIG. 43 is a chart of “Diff CA” vs. PFA fraction;

FIG. 44 is a chart of acid resistance rating vs. PFA fraction;

FIG. 45 is a chart of fusion melt point of PFA vs. PFA fraction;

FIG. 46 is a chart of second melt point of PFA vs. PFA fraction; and

FIG. 47 is a contour plot of acid resistance rating superimposed on achart of acid hours vs. fraction of PFA;

FIGS. 48-54 correspond to Example 9, wherein:

FIG. 48 is a chart of normalized ΔH of fusion of FEP vs. FEP fraction;

FIG. 49 is a chart of contact angle vs. FEP fraction;

FIG. 50 is a chart of “Diff CA” vs. FEP fraction;

FIG. 51 is a chart of acid resistance rating vs. FEP fraction;

FIG. 52 is a chart of fusion melt point of FEP vs. FEP fraction;

FIG. 53 is a chart of second melt point of FEP vs. FEP fraction; and

FIG. 54 is a contour plot of acid resistance rating superimposed on achart of acid hours vs. fraction of FEP;

FIGS. 55-61 correspond to Example 10, wherein:

FIG. 55 is a chart of normalized ΔH of fusion of MFA vs. MFA fraction;

FIG. 56 is a chart of contact angle vs. MFA fraction;

FIG. 57 is a chart of “Diff CA” vs. MFA fraction;

FIG. 58 is a chart of acid resistance rating vs. MFA fraction;

FIG. 59 is a chart of fusion melt point of MFA vs. MFA fraction;

FIG. 60 is a chart of second melt point of MFA vs. MFA fraction; and

FIG. 61 is a contour plot of acid resistance rating superimposed on achart of acid hours vs. fraction of MFA;

FIGS. 62-63 correspond to Example 11, wherein:

FIG. 62 is a chart of DH fusion 1 vs. PFA fraction;

FIG. 63 is a chart of contact angle vs. PFA fraction; and

FIG. 64 is a chart of Diff CA vs. PFA fraction.

The exemplifications set out herein illustrate embodiments of theinvention, and such exemplifications are not to be construed as limitingthe scope of the invention in any manner.

DETAILED DESCRIPTION

The present invention provides blended fluoropolymer compositions. Inone embodiment, a liquid dispersion of a first fluoropolymer is blendedwith a liquid dispersion of a second fluoropolymer. The firstfluoropolymer may be polytetrafluoroethylene (PTFE), such as a lowmolecular weight PTFE (LPTFE) that has been polymerized via a dispersionor emulsion polymerization process, and which has not been agglomerated,irradiated, or thermally degraded. The LPTFE may be in the form of anaqueous dispersion, having a mean particle size of less than 1.0 microns(μm), with the LPTFE having a first melt temperature (T_(m)) of 332° C.or less. The second fluoropolymer may be a melt processiblefluoropolymer (MPF), such as perfluoromethylvinvyl ether (MFA),fluorinated ethylene propylene (FEP), or perfluoropropylvinvyl ether(PFA), for example, in the form of an aqueous dispersion, and having amean particle size of less than 1.0 microns. Blending of the dispersionsfacilitates interaction of the LPTFE and MPF on a submicron level tofacilitate intimate blending such that, when the blended fluoropolymercomposition is dried, a crystal structure representing a true alloy ofthe fluoropolymers is formed, having melt characteristics that differfrom those of the individual fluoropolymers. The blended fluoropolymercomposition may be used to provide a coating having improvedimpermeability, stain resistance, abrasion resistance, smoothness, andhigher contact angles.

The present blended fluoropolymer compositions, upon drying or curing,have been found to include two phases, namely, a predominantly LPTFEphase and a predominantly MPF phase.

As shown in the Examples below, blended fluoropolymer compositions madein accordance with the present invention provide improved barrierproperties, as demonstrated by the ability of films cast from thesecompositions, made from blends having component ratios corresponding tomaxima in the fusion or re-melt enthalpies of the predominately MPFphase as measured by DSC, to protect aluminum panels from hydrochloricacid attack as compared to compositions that do not correspond to maximain the fusion or re-melt enthalpies.

As also shown in the Examples below, blended fluoropolymer compositionsmade in accordance with the present invention also provide improvedstain resistance, as demonstrated by powder sprayed substrates made fromfreeze dried aqueous dispersion fluoropolymer blends having componentratios corresponding to maxima in the fusion or re-melt enthalpies ofthe predominately MPF phase, as measured by DSC, as compared tocompositions that do not correspond to maxima in the fusion or re-meltenthalpies.

1. Low Molecular Weight Polytetrafluoroethylene (LPTFE).

The first fluoropolymer of the present blended fluoropolymercompositions may be a liquid dispersion of polytetrafluoroethylene(PTFE) and, in particular, may be a liquid dispersion of a PTFE having alow molecular weight (LPTFE) and/or other properties as discussed indetail below.

In one embodiment, the LPTFE is produced by a polymerization processthat is well known in the art as dispersion polymerization or emulsionpolymerization. These polymerization processes may be conducted withchain transfer agents, which reduce the average molecular weight of thefluoropolumers produced, and/or via other methods whereby thepolymerization process is controlled to form a liquid dispersion ofdirectly polymerized particles of PTFE having low molecular weight(LPTFE).

In some embodiments, the LPTFE, after being produced by dispersionpolymerization or emulsion polymerization, is thereafter notagglomerated, irradiated, or thermally degraded.

In particular, the LPTFE has not been subjected to any agglomerationsteps during its manufacture, and therefore retains a small meanparticle size as described below.

Further, in embodiments described herein, the LPTFE has not beensubjected to thermal degradation to reduce its molecular weight.

Still further, in embodiments described herein, the LPTFE has also notbeen subjected to irradiation, such as by high energy electron beam, toreduce its molecular weight. In these embodiments, the LPTFE dispersionswill not demonstrate a spectra and/or will be below a detection limitwhen subjected to electron paramagnetic resonance (EPR) or electron spinresonance (ESR) spectroscopy, as opposed to irradiated PTFE, which willdemonstrate such a spectra and/or will otherwise have detectable freeradicals.

The liquid dispersion of LPTFE in most embodiments will be an aqueousdispersion, though the LPTFE may be dispersed in other solvents and/orLPTFE originally in an aqueous phase may be phase transferred intoanother solvent, such as organic solvents including hexane, acetone, oran alcohol.

The LPTFE, when produced as described above, will typically have a meanparticle size of 1.0 microns (μm) or less, 0.9 microns (μm) or less,0.75 microns (μm) or less, 0.5 microns (μm) or less, 0.4 microns (μm) orless, 0.3 microns (μm) or less, or 0.2 microns (μm) or less. In someembodiments, the LPTFE may have a mean particle size as low as 30, 50,100, or 150 nm, or as large as 200, 250, or 350 nm, for example.

The number average molecular weight (M_(n)) of the LPTFE will typicallybe less than 500,000 and, in most embodiments, may be as low as 10,000or greater, 20,000 or greater, or 25,000 or greater, or may be as highas 200,000 or less, 100,000 or less, or 70,000 or less, 60,000 or less,or 50,000 or less, for example.

The LPTFE will have a first melt temperature (T_(m)), as determined by asuitable method such as differential scanning calorimetry (DSC), that iseither equal to or less than 332° C. In other embodiments, the firstmelt temperature of the LPTFE may be either equal to or less than 330°C., either equal to or less than 329° C., either equal to or less than328° C., either equal to or less than 327° C., either equal to or lessthan 326° C., or either equal to or less than 325° C.

The LPTFE may be provided in the form of an aqueous dispersion which iseither unstabilized or is minimally stabilized. As used herein,“unstabilized” or “minimally stabilized” refers to an aqueous dispersionthat includes less than 1.0 wt. % of a traditional surfactant, such asnon-ionic surfactant or an anionic surfactant, based on the weight ofthe LPTFE aqueous dispersion. In some embodiments, the LPTFE dispersionmay be provided in the form of an aqueous dispersion having less than1.0 wt. % surfactant, less than 0.8 wt. % surfactant, less than 0.6 wt.% surfactant, or even less than 0.5 wt. % surfactant.

The LPTFE will typically be in the form of a low molecular weight PTFEhomopolymer. However, in other embodiments, the LPTFE may include asmall amount of modifying co-monomer, in which case the PTFE is aco-polymer known in the art as “modified PTFE” or “trace modified PTFE”.Examples of the modifying co-monomer include perfluoropropylvinylether(PPVE), other modifiers, such as hexafluoropropylene (HFP),chlorotrifluoroethylene (CTFE), perfluorobutylethylene (PFBE), or otherperfluoroalkylvinylethers, such as perfluoromethylvinylehter (PMVE) orperfluoroethylvinylehter (PEVE). The modifying co-monomer will typicallybe present in an amount less than 0.1% by weight, for example, withrespect to the PTFE.

Suitable LPTFE dispersions include SFN-D, available from ChenguangR.I.C.I, Chengdu, 610036 P.R. China, as well as TE3877N, available fromDuPont. These fluoropolymers have characteristics set forth in Table 1below:

TABLE 1 Characteristics of exemplary low molecular weightpolytetrafluoroethylenes (LPTFE) Molec- Mean Surfactant Solids ularparticle (wt. %, based First melt content weight size on weight oftemperature LPTFE (wt. %) (Mn) (μm) LPTFE) (type) (DSC) (° C.) SFN-D 2510,000- 0.19 <1.0% typically 20,000 (unstabilized) between 324.5 and 326TE3877N 60 — 0.2 6% (non-ionic) 327.63

The LPTFE dispersions described above, which are provided as aqueousdispersions that are obtained via a controlled dispersion or emulsionpolymerization process to produce directly polymerized LPTFE that is notthereafter subjected to agglomeration, thermal degradation, orirradiation, will be appreciated by those of ordinary skill in the artto be distinct from other PTFE materials that are commerciallyavailable.

First, the present LPTFE dispersions are distinct from PTFE that isproduced by the polymerization process well known in the art as granularor suspension polymerization, which yields PTFE known in the art asgranular PTFE resin or granular PTFE molding powder. Granular PTFEresins will typically have a high molecular weight, such as a numberaverage molecular weight (M_(n)) of at least 1,000,000 or more and afirst melt temperature (T_(m)) greater than the 332° C., typically muchgreater than 332° C. Granular PTFE resin is typically provided in solid,powder form including particles having a mean particle size of severalmicrons, typically from 10 to 700 microns (μm). These resins may also beprovided as fine cut resins having a mean particle size of 20 to 40microns (μm), for example.

Additionally, the present LPTFE dispersions are distinct from lowermolecular weight materials prepared from high molecular weight granularPTFE resins that have been degraded by irradiation or thermaldegradation to form low molecular weight materials known as granularPTFE micropowders, which typically have a particle size ranging between2 and 20 microns (μm). Examples of granular PTFE micropowders includeZonyl® MP1200, MP1300, and MP1400 resins, available from DuPont (Zonyl®is a registered trademark of E.I. du Pont de Nemours & Co.).

Second, the present LPTFE dispersions are also distinct from highmolecular weight PTFE dispersions made from dispersion or emulsionpolymerization conducted without chain transfer agents to therebypolymerize a high molecular weight PTFE having a number averagemolecular weight (M_(n)) of at least 1,000,000 or more, and a first melttemperature (T_(m)) greater than the 332° C., typically much greaterthan 332° C. These high molecular weight PTFE dispersions are typicallystabilized with a traditional surfactant present in an amount greaterthan 1.0 wt. %, typically much greater than 1.0 wt. %.

Additionally, the present LPTFE dispersions are also distinct from highmolecular weight PTFE dispersions that are produced via dispersion oremulsion polymerization and thereafter coagulated or agglomerated. Stillfurther, the present LPTFE dispersions are distinct from high molecularweight PTFE dispersions that are produced via dispersion or emulsionpolymerization and thereafter coagulated or agglomerated, and then aresubjected to thermal degradation or irradiation to form low molecularweight PTFE powders, known in the art as PTFE micropowders, which areprovided as solid powders having a particle size between 2 and 20microns (μm), such as for use in extrusion and other applications.Examples of PTFE micropowders include Zonyl® MP1000, MP1100, MP1500 andMP1600 resins, available from DuPont (Zonyl® is a registered trademarkof E.I. du Pont de Nemours & Co.).

Third, the present LPTFE dispersions are also distinct from LPTFEmicropowders that are polymerized via dispersion or emulsionpolymerization in the presence of chain transfer agents, and then areagglomerated to form PTFE micropowders having an average particle sizeof between 2 and 20 microns (μm), for example.

2. Melt Processible Fluorpolymers (MPF).

The second fluoropolymer may be a liquid dispersion of a meltprocessible fluoropolymer (MPF), such as perfluoromethylvinvyl ether(MFA), perfluoroethylvinyl ether (EFA), fluorinated ethylene propylene(FEP), or perfluoropropylvinvyl ether (PFA), for example.

Similar to the LPTFE discussed above, the MPF may be produced by apolymerization process that is well known in the art as dispersionpolymerization or emulsion polymerization. These polymerizationprocesses may be conducted with chain transfer agents, which reduce theaverage molecular weight of the fluoropolumers produced, and/or viaother methods whereby the polymerization process is controlled to form aliquid dispersion of directly polymerized particles of MPF.

In most embodiments, the MPF, after being produced by dispersionpolymerization or emulsion polymerization, is thereafter notagglomerated, irradiated, or thermally degraded. In particular, the MPFwill not have been subjected to any agglomeration steps during itsmanufacture, and therefore retains a small mean particle size asdescribed below.

The liquid dispersion of MPF in most embodiments will be an aqueousdispersion, though the MPF may be dispersed in other solvents and/or MPForiginally in an aqueous phase may be phase transferred into anothersolvent, such as organic solvents including hexane, acetone, or analcohol.

The MPF, when produced as described above, will typically have a meanparticle size of 1.0 microns (μm) or less, 0.9 microns (μm) or less,0.75 microns (μm) or less, 0.5 microns (μm) or less, 0.4 microns (μm) orless, 0.3 microns (μm) or less, or 0.2 microns (μm) or less. Inparticular, the MPF may have a mean particle size as low as 30, 50, 100,or 150 nm, or as large as 200, 250, or 350 nm, for example.

The MPF may also be provided in the form of an aqueous dispersion whichis either unstabilized or is minimally stabilized. As used herein,“unstabilized” or “minimally stabilized” refers to an aqueous dispersionthat includes less than 1.0 wt. % of a traditional surfactant, such asnon-ionic surfactant or an anionic surfactant, based on the weight ofthe MPF aqueous dispersion. In some embodiments, the MPF dispersion maybe provided in the form of an aqueous dispersion having less than 1.0wt. % surfactant, less than 0.8 wt. % surfactant, less than 0.6 wt. %surfactant, or even less than 0.5 wt. % surfactant.

Typically, the melt flow rate (MFR) of the MPF will be greater than 4g/10 min, as determined by ASTM D1238.

Also, the MPF will typically have a co-monomer content, i.e., a contentof one or more monomers other than tetrafluoroethylene (TFE), of about3.0 wt. % or greater, such as 4.0 wt. % or greater, 4.5 wt. % orgreater, 5.0 wt. % or greater, 5.5 wt. % or greater, or 6.0 wt. % orgreater.

Suitable MPF dispersions include TE7224 (PFA), available from DuPont,6900Z (PFA), available from Dyneon LLC, TE9568 (FEP), available fromDuPont, Neoflon ND-110 (FEP), available from Daikin, and Hyflon XPH6202-1 (MFA), available from Solvay. These MPF dispersions havecharacteristics set forth in Table 2 below:

TABLE 2 Characteristics of exemplary melt processible fluoropolymers(MPF) Mean Solids particle Melt flow First melt content size rate (MFR)temperature MPF (type) (wt. %) (μm) (g/10 min) (DSC) (° C.) DuPont 58.60.26 2.4 313.0 (shoulder TE7224 (PFA) 321.2) Dyneon 6900Z 49.4 0.31 19.4310.25 (PFA) DuPont 55.6 0.17 11.9 257.84 TE9568 (FEP) Daikin 56.5 0.16— 232.83 Neoflon ND- 110 (FEP) Solvay Hyflon 27.2 0.28 4.5 306.31(shoulder XPH 6202-1 287.29) (MFA)

3. Blended Fluoropolymer Compositions.

To form the blended fluoropolymer compositions of the present invention,a LPTFE liquid dispersion and a MPF liquid dispersion are blendedtogether. When liquid dispersions are used, the dispersions may havevarying solids contents, and one of ordinary skill in the art willrecognize that the wet weights of the liquid LPTFE and MPF dispersionsmay be selected based on the solids contents of the dispersions and thedesired relative weight percent ratio of the LPTFE and MPF that isdesired in the resulting blended compositions.

Notably, because the LPTFE and the MPF are provided in the form ofliquid dispersions having the small mean particle sizes set forth above,upon blending of the dispersions particles of the LPTFE and MPF arebrought into contact with each other at the submicron level, prior tolater processing steps in which the dispersions are dried or melted, forexample. As discussed above, the LPTFE and MPF are not agglomeratedprior to blending, such that the submicron interaction of the LPTFE andMPF is thought to facilitate the formation of the highly crystallineform of the dried or cured fluoropolymer blend that is believed to beimportant to achieving the beneficial results obtained with the presentblended compositions.

In particular, it is thought that the blended fluoropolymer compositionsof the present invention, and the manner of blending same, results in abetter packing of the LPTFE and MPF in the MPF crystal phase. Asdiscussed in the Examples below, in one embodiment, optimal packing ofthe crystals for any LPTFE or MPF may be determined by finding themaximum melting point of the re-melt peak and/or the maximum normalizedheat of fusion/2nd melt for the MPF phase of the two components underexamination by DSC. Furthermore, as also discussed in the Examplesbelow, the compositions associated with these maxima also correspond topeaks in the contact angle data and acid etch resistance of thesematerials.

The relative ratios, fractions, or weight percents of the LPTFE and MPFin the blended fluoropolymer compositions described herein are based onthe total weight of the LPTFE and MPF fluoropolymers, excluding otherfluoropolymers other than LPTFE and MPF as well as non-fluoropolymercomponents that may be present, such as water or other solvents,surfactants, pigments, fillers, and other additives.

The LPTFE may comprise as little as 5 wt. %, 10 wt. %, or 15 wt. %, oras much as 85 wt. %, 90 wt. %, or 95 wt. % by weight of the blendedcomposition. In one embodiment, the LPTFE may comprise between 40 wt. %and 60 wt. % of the blended composition, such as 50 wt. % of the blendedcomposition. The MPF may comprise as much as 85 wt. %, 90 wt. %, or 95wt. %, or as little as 5 wt. %, 10 wt. %, or 15 wt. % by weight of theblended composition. In one embodiment, the MPF may comprise between 40wt. % and 60 wt. % of the blended composition, such as 50 wt. % of theblended composition.

The following are exemplary content ranges for the MPF and LPTFEfluoropolymers in blends of the present invention that, as will beapparent from the Examples below, have been found to embody thebeneficial characteristics of the present invention. The content rangesset forth below are inclusive of all intermediate integer values.

Blends of LPTFE and MFA may include, in one embodiment, from 35 wt. % to90 wt. % MFA and from 10 wt. % to 65 wt. % LPTFE. In another embodiment,such blends may include from 45 wt. % to 76 wt. % MFA and from 24 wt. %to 65 wt. % LPTFE. In another embodiment, such blends may include from56 wt. % to 76 wt. % MFA and from 24 wt. % to 44 wt. % LPTFE. In anotherembodiment, such blends may include from 63 wt. % to 70 wt. % MFA andfrom 30 wt. % to 37 wt. % LPTFE. In a further embodiment, such blendsmay include 67 wt. % MFA and 33 wt. % LPTFE.

Blends of LPTFE and FEP may include, in one embodiment, from 25 wt. % to90 wt. % FEP and from 10 wt. % to 75 wt. % LPTFE. In another embodiment,such blends may include from 35 wt. % to 90 wt. % FEP and from 10 wt. %to 65 wt. % LPTFE. In another embodiment, such blends may include eitherfrom 35 wt. % to 55 wt. % FEP and from 45 wt. % to 65 wt. % LPTFE, orfrom 60 wt. % to 90 wt. % FEP and from 10 wt. % to 40 wt. % LPTFE. Inanother embodiment, such blends may include either from 40 wt. % to 50wt. % FEP and from 50 wt. % to 60 wt. % LPTFE, or from 75 wt. % to 85wt. % FEP and from 15 wt. % to 25 wt. % LPTFE. In a further embodiment,such blends may include either 50 wt. % FEP and 50 wt. % LPTFE, or 75wt. % FEP and 25 wt. % LPTFE.

Blends of LPTFE and PFA may include, in one embodiment, from 37 wt. % to80 wt. % PFA and from 20 wt. % to 63 wt. % LPTFE. In another embodiment,such blends may include from 37 wt. % to 65 wt. % PFA and from 35 wt. %to 63 wt. % LPTFE. In another embodiment, such blends may include from43 wt. % to 63 wt. % PFA and from 37 wt. % to 57 wt. % LPTFE. In anotherembodiment, such blends may include from 50 wt. % to 60 wt. % PFA andfrom 40 wt. % to 50 wt. % LPTFE. In a further embodiment, such blendsmay include 53 wt. % PFA and 47 wt. % LPTFE.

Aqueous dispersions of the first and second fluoropolymers may beblended with slow stirring, for example, or via another low or mediumshear method which minimizes the potential for agglomeration,coaglulation, or fibrillation of the fluoropolymer particles.

The blended fluoropolymer compositions may be used in the form of ablended dispersion, such as part of a wet coating system which isapplied to a substrate and subsequently cured, such as by heat curing,to form a coating of film. The blended fluoropolymer compositions maythemselves comprise the coating or film, or may be a component of a morefully formulated coating system which includes other components. Also,the blended fluoropolymer compositions may themselves be, or may be acomponent of, a primer coating which is applied directly to the surfaceof a substrate, and/or may themselves be, or may be a component of, anovercoat which is applied over a primer coating.

The blended fluoropolymer compositions will typically be heat cured, butmay also be dried, such as by water evaporation, freeze drying, or spraydrying, for example, to form blended powders. The blended fluoropolymersmay be used as powders and/or may be formed into solid pellets that maybe used to manufacture extruded articles such as wire, cable, fuel hoseliners or other tubing, and injection moldable items.

The blended fluoropolymer compositions may also include auxiliarycomponents or additives, such as fillers, reinforcement additives,pigments, and film formers, if desired, depending on the end useapplication of the blended fluoropolymer compositions.

4. Freeze Drying of the Blended Fluoropolymer Compositions.

In drying a blended fluoropolymer dispersion made in accordance with thepresent invention using freeze drying, the blended dispersion is frozenin a freezer at a temperature below 0° C., such as at a temperature inthe range of −60° C. to −20° C. Typically, freezing might be completedin 6 hrs to 24 hrs. The blended aqueous dispersion may be poured,scooped or otherwise transferred into a tray prior to freezing, and thetray is then placed into the freezer and frozen within the tray.

The fluoropolymer dispersions may be aqueous, with or without surfactantand with or without bridging solvents (organic solvent used to aid thedispersion/solvating of additional resins). If bridging solvents areused, they should be at concentrations low enough and have high enoughmelting points so that freezing is not inhibited.

Then, sublimation is carried out, such as by using sub-atmosphericpressure or a vacuum. The use of a reduced pressure causes sublimationof the carrier from a frozen state directly to a gaseous state, avoidingthe solid to liquid and liquid to gas transition. The reduced pressuremay be created by means of a vacuum pump, for example, in the range 0.01atm to 0.99 atm, or 0.04 atm to 0.08 atm. Typically, sublimation mightbe completed in 12 hrs to 48 hrs.

The freeze drying may be carried out at a temperature which is inpractice below the glass transition temperature of the fluoropolymer.The glass transition temperature, T_(g), of a polymer is the temperatureat which it changes from a glassy form to a rubbery form. The measuredvalue of T_(g) will depend on the molecular weight of the polymer, itsthermal history and age, and on the rate of heating and cooling. Typicalvalues are MFA about 75° C., PFA about 75° C., FEP about −208° C., PVDFabout −45° C. Also, the temperature may be controlled to assist thesublimation process and avoid melting of the carrier liquid. It is abeneficial coincidence that these controls also maintain temperaturesbelow the Tg values for some of the materials listed. Thus, the methodmay be carried out at ambient temperature. Alternatively, the method maybe carried out at a temperature above ambient temperature, in order toreduce the time taken to complete the process.

The blended fluoropolymer composition may be treated after sublimationhas occurred or at any point during the process of the presentinvention. Such modifications may include, milling or irradiation of thefluoropolymer composition. Irradiation of the fluoropolymer compositionwould generally be carried out after milling to assist in particle sizecontrol. Milling adjusts the particle size distribution of thefluoropolymer composition, for example reducing the mean particle sizeto produce a finer powder. Typically the milling would be carried outconventionally in a pin or jet mill.

Where the method additionally comprises irradiation of the modifiedfluoropolymer particles, this would typically be carried out on thepowder, but alternatively on the dispersion. Irradiation adjusts themelt characteristics of the modified fluoropolymer, for example to lowerthe melting temperatures/glass transition temperatures and increase themelt flow rate. Irradiation of fluoropolymer dispersions is discussed inU.S. Pat. No. 7,220,483, the disclosure of which is expresslyincorporated herein by reference.

The freeze drying method does not result in the tight agglomeration ofthe particles, but instead produces a fine powder, which is suitable foruse in extrusion, conventional powder spray application techniques orfor redispersion in aqueous or organic media. The friable powder can bebroken down easily for particle size modification. The method may becarried out at a temperature below the glass transition temperature ofthe fluoropolymer, in contrast to the known processes involving spraydrying and coagulation, which require temperatures well in excess of100° C. The use of ambient temperature allows greater energy efficiency,while the use of temperatures that are above ambient temperature, butbelow the glass transition temperature, can be used to increase thespeed with which the sublimation proceeds. Temperatures above ambientcan also be used to assist secondary drying, to drive off any remainingliquid carrier traces.

The freeze drying method can be used to prepare a modified fluoropolymerpowdered material whether the fluoropolymer would tend to befibrillatable or non-fibrillatable. A fibrillatable polymer is one whichforms fibers when exposed to a shear force. The known methods, whichinvolve spray drying and coagulation, both expose the solidfluoropolymer particles to shear forces, which can result in theproduction of an intractable material. The present invention does notinvolve shear forces at any stage and is therefore suitable for use witha fibrillatable fluoropolymer. The method may be used to prepare amodified fluoropolymer powdered material from a pumpable or non-pumpablesuspension of the solid fluoropolymer particles in a liquid carrier. Thedispersion may be non-pumpable because of high viscosity or shearsensitivity. The method does not involve any steps where the suspensionmust be pumped. Instead, the dispersion may be poured or scooped intothe tray for freezing, and the solid, frozen block may be transferredinto the vacuum chamber.

EXAMPLES

The following non-limiting Examples illustrate various features andcharacteristics of the present invention, which is not to be construedas limited thereto. Throughout the Examples and elsewhere herein,percentages are by weight unless otherwise indicated.

Several of the Figures herein were originally prepared in color, andincluded characters of varying color to represent data points associatedwith different types or grades of LPTFE and/or MPF materials that weretested, in order to distinguish data associated with the different typesor grades of such materials. The Figures are now presented herein inblack and white to primarily illustrate trends in the data based on thecollection of data points, and without need to associate the variouscharacters and data points with the particular types or grades of LPTFEand/or MPF materials that were used.

Introduction to Examples 1-5

Examples 1-3 present three data sets for blends of LPTFE (SFN-D,Chenguang) with each of PFA (du Pont PFA TE7224, Lot#0804330005,Solids=58.6%) (Example 1); FEP (DuPont FEP dispersion TE9568,Lot#080333032, Solids=55.6%) (Example 2); and PFA (Solvay Hyflon MFA XPH6202-1, Lot#Lab, Solids=27.2%) (Example 3). The data presented wasobtained using differential scanning calorimetry (DSC) and, in mostcases, individual data points in the Figures were each taken from DSCcurves.

In Examples 1-3, ‘normalized’ means data that is normalized for thefraction of the given component in the original mixture, i.e., for theSFN-D phase the normalized SFN-D data is given by, {SFN-Ddata}/(1−[MPF]).

The preparation of blended fluoropolymer compositions for Examples 1-4is outlined as follows. The given amounts of aqueous fluoropolymerdispersions are mixed under air in a mixer for 30 minutes to ensurehomogenous mixture of the dispersions. The mixture is mixed under low tomedium shear to avoid coagulation of blended dispersion. A plasticeye-dropper is used to place a known weight of the mixed, blendeddispersion into a pre-weighed drying dish. The dispersion is flashed at100° C. in an oven for 30 minutes, and the residual powder is then driedat 200° C. for an additional 30 minutes. After the dried powder iscooled to room temperature, the powder is weighed and the wt. % solidsin the mixed dispersion is calculated. The blended fluoropolymer powderis then ready for DSC analysis.

For DSC analysis, 10 mg (+/−1 mg) of the dried powder is placed in aaluminum DSC sample pan, and the pan is sealed with a standard lid. Theheating and cooling cycles of the DSC are as follows: (1) ramp 15.0°C./min to 400° C.; (2) isothermal for 1.00 min; (3) ramp 15.0° C./min to135° C.; (4) isothermal for 1.00 min; (5) ramp 15.0° C./min to 400° C.;and (6) air cool.

The melting peaks are obtained during the (1) ramping up heatingprocess. The crystallization peaks are obtained in the (3) coolingprocess. The 2nd melting peaks are obtained at the (5) heating process.

Example 1 MFA/LPTFE Blends

Samples of MFA/SFN-D blends were obtained from a variety of sourcesincluding powders formed by freeze drying, dried mixed dispersions, andscraped dried films. The initial form of the blend did not influence theobservations.

The main observation made in the DSC for these materials is the factthat there is a maximum in the re-melt and fusion peaks for the MFAphase which corresponds with a maximum in the observed melting points aswell. These maxima occur at a composition known to give the beneficialeffects of the present invention (i.e., at approximately 65%-75% [MFA];see FIGS. 1-5) and are believed to be characteristic of it. In thesecompositions the SFN-D phase also yields higher melt enthalpies relativeto pure SFN-D however in this case the melting points are lower (FIGS.8-11). It appears that both phases experience an increase incrystallinity under these conditions and in the case of the MFA phase itappears that this may be associated with denser crystals. In otherwords, the compositions of both phases appear to be more crystalline.This will undoubtedly improve permeability resistance and is alsoexpected to lower surface energy (reducing staining etc).

When all the MFA data are fitted there is a maximum in the re-melt peakof the MFA phase both for peak area (heat of melting) and melting pointat approximately 70% MFA which corresponds to the desired properties.The heat of fusion data appears to shift its peak to slightly lower MFAcontent. This may be due to incomplete mixing of the first and secondfluoropolymers at the first melting point, but may be more likely due toan apparent shift in melting point when the sample is heated vs. cooled.

The non-normalized data is shown FIGS. 6-9 and shows the same maximum inthe ΔH 2^(nd) melt curve.

Considering FIGS. 1-4 and FIGS. 9-10 it can be seen that both the LPTFEphase and the MFA phase experience increased in crystallinity atcompositions between 65-75% MFA.

Example 2 FEP/LPTFE blends

With respect to FEP, it appears that there might be 2 peaks in the FEPphase melt and fusion enthalpy curves, at approximately 40% and atapproximately 80% [FEP]. Similarly, there are also apparently 2 peaks inthe SFN-D phase, but these occur at slightly different compositions,i.e., at approximately 35% and at approximately 75% [FEP] (see FIGS. 18and 19).

By analogy with the MFA blends of Example 1, it would seem reasonable toassume that the beneficial effects of the present invention might beobserved at approximately 40% [FEP] and possibly at approximately 80%[FEP]. The various melting points show peaks in similar regions as wasthe case in the MFA of Example 1 (FIGS. 14, 15, 18, and 19).

If we examine the FEP/SFN-D blends we see that in the 2^(nd) melttemperature of the FEP phase there appears to be at a minimum for 70%FEP but there is a peak at 50% [FEP]. There also appears to be a peak inthe AH for 2^(nd) melt and in the fusion data at 80-90% (FIGS. 16 and17).

Also, the melting point of the SFN-D phase decreases after a second FEPphase (denoted by +marker in FIG. 12) starts to appear in the re-meltbut in the case for MFA shown above this decrease is seen before thesecond phase occurs (FIG. 8). Examination of the enthalpies shows thatthere are 2 peaks in both the SFN-D phase (at 50% and 80% FEP) and inthe FEP phase (at 40% and at least 80% FEP)(FIGS. 16 and 17). Blends of40-60% FEP and 80-90% FEP might be expected to show properties inaccordance with the beneficial effects of the present invention.

Example 3 PFA/LPTFE Blends

PFA data appears to be somewhat more difficult to analyze due todifficulties in resolving some peaks which are clearly overlapping,especially for the re-melt peaks. Nevertheless the fusion enthalpy curveexhibits a peak in the data at approximately 50% PFA as well asindicating the potential for a further peak at ca. 80% (see FIGS. 21 and23).

An observation of note was made when films were cast from the dispersionPFA/SFN-D blends onto Al plates and acid etched with concentrated HCl.It was clearly evident that the 50% and 60% PFA blends did not revealmuch, if any, penetration whereas the other compositions showedsignificant breakthrough to the substrate (see FIG. 26A). The presentinventors hypothesize that this is clear and unequivocal evidence that,as anticipated, peaks in the melt/fusion enthalpy curves occur atcompositions associated with the beneficial effects of the presentinvention, which in this case is demonstrated by reduced permeability.This observation was further reinforced by contact angle measurementswhich appear to show a maximum value in a similar range of composition(FIG. 26B).

For PFA it appears possible that second PFA phase peaks occur so closeto the primary SFN-D melt/fusion peaks that they are difficult toseparate and characterize though there are indications that these secondpeaks are present. Nevertheless similarly to both MFA and FEP the SFN-Dphase does show a reduction in melting point with increasing [PFA] whichgives further reason to believe that the so far uncharacterized PFApeaks are there, and at the very least demonstrates that the PFA isaffecting the SFN-D phase.

The apparent heat of fusion and 2^(nd) melt ΔH for the SFN-D phaseincreases with increasing [PFA] but this might be misleading; it couldbe caused by the undetected PFA melt peak hidden beneath. In fact sincethis polymer blend is the only one to show such an increase innormalized SFN-D peak area with increasing [MPF] (at least above 50%MPF), it appears to indicate that there is a separate (hidden to DSC)PFA phase. However, further examination of the fusion data has shown apeak at ca 50% PFA and the beneficial properties of the presentinvention have been observed for this blend

Example 4

FIGS. 27-34 summarize the differences in location, with respect to theinventive compositions, of the MPF phase fusion and melt enthalpy curvesclearly indicate the maxima for each MPF (FIGS. 27, 28) whereas thecorresponding SFN-D phase for PFA and MFA appear to be shifted on the[MPF] axis by amount equivalent to the difference in [MPF] of the MPFphase peaks (FIGS. 29, 30). A similar shift is found for the SFN-Dfusion and 2^(nd) melt temperatures (FIGS. 31, 32).

Examination of FIGS. 27-34 shows that the PFA curves are shiftedrelative to the MFA curves by between 10-20% towards lower [MPF].Comparing the regions for the beneficial effects of the presentinvention between Examples 1 and 3 a strong correlation is observed. InPFA, this occurs at approximately 50% PFA and with MFA at approximately70%. FEP possibly shows two regions as well, one at approximately 40%FEP and another possibly at >80% FEP.

Example 5 PTFE/MFA Blend

An SFN-DN PTFE aqueous dispersion stabilised with 0.6% D6483 (100%polysiloxane) on PTFE solids was added to MFA 6202-1 MFA dispersion togive 25:75 PTFE:MFA solids content. The dispersions were mixed with slowstirring. The mixture was frozen and freeze-dried. The resulting drypowder was applied by electrostatic spray gun over a Xylan 4018/G0916primer on to a grit blasted aluminum panel. The panel was flashed off at150° C. and cured at 400° C. for 20 minutes. The powder melted to form acontinuous film.

Reference is now made to three DSC data sets in FIGS. 35-37. Acomparison of the melting point shift from pure polymers (FIG. 35-MFAand FIG. 36-PTFE) to the alloy (25 PTFE, 75 MFA) FIG. 37, show that thepolymers form a true alloy and co-crystallize together.

The MFA/PTFE blend produced by this process has certain advantages.Increasing the crystalline nature of the MFA polymer can be demonstratedby considering the heat of fusion in the DSC data. The high crystallinepolymer has better barrier properties. Also, the freeze-drying processyields a homogenous blend of PTFE and MFA. Mixing on a nano scale andfreeze drying locks polymer particles in place; no macro aggregation ofindividual polymer components occurs.

Example 6 Lap Shear Test of PTFE/MFA Blend

In this Example, the release properties of coatings made with a controlPFA fluoropolymer and with a blended LPTFE/MFA fluoropolymer made inaccordance with the present invention were investigated. The test methodused for evaluation was ASTM D1002 (Standard Test Method for ApparentShear Strength of Single-Lap-Joint Adhesively Bonded Metal Specimens byTension Loading (Metal-to-Metal)), which test method was modified asdiscussed below.

The control fluoropolymer was Daikin ACX-31 PFA powder. An experimentalblended fluoropolymer powder was made by blending an MFA dispersion(Solvay Hyflon MFA XPH 6202-1, 27.2% solids) and an LPTFE dispersion(SFN-D, 25% solids) followed by freeze drying to give a 75:25 wt. %ratio of MFA:PTFE in the resulting powder.

Sample panels of gritblasted aluminium were prepared and then treatedwith Xylan 80-178/G3435 metallic black primer followed by flashing offat 150° C. and allowing to cool. The control and experimental powderswere applied by electrostatic powder spray and then cured at 400° C. for15 minutes. The gritblasting pretreatment used for the coated panels wasone method improvement, ensuring a consistent coated surface which inturn gave less scatter in results. Using freshly coated panels gavegreater consistency rather than re-using test panels.

The aluminium plates used were 1″ wide×4″ long. One plate was coated anda second plate was solvent wiped using ethanol. One improvement to thetest method was the careful preparation of the panels for testing toensure that there were no differences in procedure between the two setsof panels. PSI-326 (Polymeric Systems Inc.) epoxy adhesive was mixed 1:1w/w for approximately 45 seconds and then applied to both surfaces. Theplain aluminium panel received the larger proportion with the coatedplates being smeared until full wet out was observed. Solid sphericalglass beads of nominal 0.6 mm were scattered onto the aluminium plate.

The test was performed using PSI 326 epoxy adhesive. Pairs of plateswere aligned and firmly clamped together using strong spring clips asshown in FIG. 38. The coated panel and adhesive overlap is 1 in². Thethickness of the epoxy/adhesive bond was set using glass beads (0.6 mm).The adhesive was hand mixed and applied to the panels which were thenclamped together. The panels were left to stand for 72 hours prior totesting on the Lloyd Tensometer. The use of clamps was anotherimprovements to the test method. A further improvement included removalof excess adhesive immediately without disturbing the bond. Clampedplates were left for 72 hours undisturbed before testing.

The following results were obtained:

TABLE 3 Control fluoropolymer Panel # Pull-apart force (N) 1 185 2 235 3216 4 158

TABLE 4 Experimental blended fluoropolymer Panel # Pull-apart force (N)1 95.1 2 81.3 3 94.0 4 83.0

As is clear from the foregoing, the coatings made with the experimentalblended fluoropolymer displayed better release characteristics than thecoatings made with the control fluoropolymer, as evidence byapproximately 50% lesser pull-apart forces.

Example 7 Stain Resistance

In this example, the stain resistance of coatings made with a controlPFA fluoropolymer and with a blended LPTFE/MFA fluoropolymer made inaccordance with the present invention were investigated.

The control fluoropolymer was Daikin ACX-31 PFA powder. An experimentalblended fluoropolymer powder was made by blending an MFA dispersion(Solvay Hyflon MFA XPH 6202-1, 27.2% solids) and an LPTFE dispersion(SFN-D, 25% solids) followed by freeze drying to give a 75:25 wt. %ratio of MFA:PTFE in the resulting powder.

Two aluminum panels treated with Xylan 80-178/G3435 metallic blackprimer followed by flashing off at 150° C. and allowing to cool. Thecontrol and experimental powders were applied by electrostatic powderspray and then cured at 400° C. for 10 minutes, specifically, the panelswere coated as shown in FIG. 39, with each panel coated on its left sidewith the control coating and on its right side with the experimentalcoating.

Referring to FIG. 39, six stain-prone materials, including sugar water(A-1), worchestershire sauce and sugar (B-1), honey BBQ sauce (C-1),tomato sauce and sugar (D-1), soy sauce and sugar (E-1), and orangejuice (F-1) were dropped onto each side of the panels, and then bakedonto each of the control and experimental coatings at 205° C. for 30minutes. Once cooled, each panel was then turned upside down and tappedonce lightly. The improvement in stain resistance exhibited by the rightsides of each panel that were coated with the experimental coating canbe seen from FIGS. 39 and 40, although no improvement was observed forsoy sauce and sugar (E-1).

Introduction to Examples 8-10

Further Examples of MPF/LPTFE blends are given below where more detailedexamination of thermal data, contact angles and acid resistance wasconsidered.

The data is summarized in Table 5 below, in which the columns areexplained as follows:

-   -   “MPF %” and “LPTFE %” are the fractions of the MPF and LPTFE        components by weight, i.e., 0.1 is 10 wt. %.    -   “CA” is the contact angle are for a water droplet in degrees, as        determined using the “Drop Shape Analysis” system (DSA10),        available from Kruss GmbH of Hamburg, Germany, according to the        Young Relation.    -   “Diff CA” is the difference in contact angle for a given        component/mixture from a linear interpolation of the contact        angles for that of the pure MPF and LPTFE components, in        degrees.    -   “Mpt” refers to melting point, in degrees C., using the DSC        procedure set forth below.    -   Acid rating scale is on a 0.1-1 scale according to the procedure        set forth below, where 1 represents excellent acid resistance as        judged by photographic examination.    -   Enthalpies (“DH”) are in J/g.

Examples 10-12 respectively present three data sets for blends of LPTFE(SFN-D, Chenguang) with each of a first PFA, referred to in Table 13below as “PTFE (A)” (Dyneon PFA6900Z Lot#38C1998X, Solids=49.4%) asecond PFA, referred to in Table 13 below as “PTFE (B)” (du Pont PFATE7224, Lot#0804330005, Solids=58.6%) (Example 10); FEP (Neoflon FEPND-110 Dispersion, Lot#ND110R86001, Solids 56.5%) (Example 11); and MFA(Solvay Hyflon MFA XPH 6202-1, Lot#Lab, Solids=27.2%) (Example 12).

The data presented was obtained using differential scanning calorimetry(DSC) and, in most cases individual data points in FIGS. 41-64 were eachtaken from DSC curves.

In Examples 10-12, ‘normalized’ means data that is normalized for thefraction of the given component in the original mixture, i.e., for theLPTFE (SFN-D) phase the normalized SFN-D data is given by, {SFN-Ddata}/(1−[MPF]).

The blended fluoropolymer compositions for Examples 10-12 were preparedas follows. The given amounts of aqueous fluoropolymer dispersions weremixed under air in a mixer for 30 minutes to ensure homogenous mixtureof the dispersions. The mixture was mixed under low to medium shear toavoid coagulation of blended dispersion. A plastic eye-dropper was usedto place a known weight of the mixed, blended dispersion into apre-weighed drying dish. The dispersion was flashed at 100° C. in anoven for 30 minutes, and the residual powder was then dried at 200° C.for an additional 30 minutes. After the dried powder cooled to roomtemperature, the powder was weighed and the percent solids in the mixeddispersion was calculated. The blended fluoropolymer powder was thenready for DSC analysis.

For DSC analysis, 10 mg (+/−1 mg) of the dried powder was placed in aaluminum DSC sample pan, and the pan was sealed with a standard lid. Theheating and cooling cycles of the DSC were as follows: (1) ramp 15.0°C./min to 400° C.; (2) isothermal for 1.00 min; (3) ramp 15.0° C./min to135° C.; (4) isothermal for 1.00 min; (5) ramp 15.0° C./min to 400° C.;and (6) air cool.

The melting peaks were obtained during the (1) ramping up heatingprocess. The crystallization peaks were obtained in the (3) coolingprocess. The 2nd melting peaks were obtained at the (5) heating process.

The panel preparation method for contact angle and acid resistancetesting was as follows:

1. Make liquid blend of MPF and LPTFE in the desired ratios.

2. Add the appropriate formulation to the blend created in step 1. Usethe following formulations and percentages to make the blends fordrawdown.

3. Blend the mix gently to avoid air bubbles.

4. Using a pipet apply a small amount to an aluminum degreased panel.

5. Draw the coating down the panel in a smooth motion using a 3 mil wetpath bird applicator.

6. Flash the panel for approximately 5-10 minutes at 200° F.

7. Move the panel to 400° F. and flash an additional 5 minutes.

8. Cure the panel for 10 minutes at 750° F.

The acid etch test procedure was as follows:

1. Trim the panel to fit into the largest petri dish with lid available.

2. Apply 6000 uL of 36.5-38% concentrated HCl in two different locationson the panel to account for any possibility of inconsistent film build.

3. Carefully place the panel with HCl into the petri dish.

4. Cover the petri dish with the lid and seal using vacuum grease.

5. Take pictures of the panels every hour for 8 hours.

6. Rate the pictures at the end of the 6 hours using the rating scale of0.1-1 (0.1 worst-1 best).

The results are presented below in Table 5:

TABLE 5 MPF/LPTFE Blends Acid 2nd 2nd Norm Norm rating Fusion Fusionmelt melt DH DH MPF Diff (0-1 mpt mpt mpt mpt Fusion Remelt Type MPF %LPTFE % CA CA scale) MPF LPTFE MPF LPTFE MPF MPF FEP 0 1.00 133.97 −0.230.1 — 310.55 — 326.67 0.0 0.0 FEP 0 1.00 134.02 −0.18 0.1 — 310.55 —326.67 0.0 0.0 FEP 0 1.00 134.62 0.42 0.1 — 310.55 — 326.67 0.0 0.0 FEP0.1 0.90 130.64 −1.96 0.1 — 310.45 — 326.9 0.0 0.0 FEP 0.1 0.90 130.65−1.95 0.1 — 310.45 — 326.9 0.0 0.0 FEP 0.1 0.90 129.21 −3.39 0.1 —310.45 — 326.9 0.0 0.0 FEP 0.2 0.80 126.69 −4.31 0.6 — 310.5 — 326.870.0 0.0 FEP 0.2 0.80 127.53 −3.47 0.6 — 310.5 — 326.87 0.0 0.0 FEP 0.20.80 129.21 −1.79 0.6 — 310.5 — 326.87 0.0 0.0 FEP 0.4 0.60 129.77 1.981 213.96 309.99 232.56 326.46 8.0 9.9 FEP 0.4 0.60 129.77 1.98 1 213.96309.99 232.56 326.46 8.0 9.9 FEP 0.4 0.60 129.54 1.75 1 213.96 309.99232.56 326.46 8.0 9.9 FEP 0.45 0.55 129.78 2.79 1 213.35 309.9 233.1326.08 11.6 10.9 FEP 0.45 0.55 129.55 2.56 1 213.35 309.9 233.1 326.0811.6 10.9 FEP 0.45 0.55 128.43 1.44 1 213.35 309.9 233.1 326.08 11.610.9 FEP 0.5 0.50 127.38 1.19 1 212.62 309.48 232.87 325.93 16.4 9.9 FEP0.5 0.50 128.90 2.71 1 212.62 309.48 232.87 325.93 16.4 9.9 FEP 0.5 0.50130.16 3.97 1 212.62 309.48 232.87 325.93 16.4 9.9 FEP 0.55 0.45 126.951.56 0.9 212.6 309.41 233.53 325.42 13.2 9.5 FEP 0.55 0.45 128.54 3.150.9 212.6 309.41 233.53 325.42 13.2 9.5 FEP 0.55 0.45 126.89 1.50 0.9212.6 309.41 233.53 325.42 13.2 9.5 FEP 0.6 0.40 127.92 3.34 0.5 214.36309.4 233.45 325.24 11.7 11.0 FEP 0.6 0.40 127.60 3.02 0.5 214.36 309.4233.45 325.24 11.7 11.0 FEP 0.6 0.40 127.38 2.80 0.5 214.36 309.4 233.45325.24 11.7 11.0 FEP 0.7 0.30 126.75 3.77 0.4 215.51 308.69 235.16325.16 12.4 9.3 FEP 0.7 0.30 125.96 2.98 0.4 215.51 308.69 235.16 325.1612.4 9.3 FEP 0.7 0.30 126.23 3.25 0.4 215.51 308.69 235.16 325.16 12.49.3 FEP 0.8 0.20 122.48 1.10 0.2 215.21 307.93 234.79 324.63 15.1 10.9FEP 0.8 0.20 122.61 1.23 0.2 215.21 307.93 234.79 324.63 15.1 10.9 FEP0.8 0.20 123.87 2.49 0.2 215.21 307.93 234.79 324.63 15.1 10.9 FEP 0.90.10 119.87 0.10 0.1 218.96 306.42 235.27 325.49 15.7 11.6 FEP 0.9 0.10116.29 −3.48 0.1 218.96 306.42 235.27 325.49 15.7 11.6 FEP 0.9 0.10120.07 0.30 0.1 218.96 306.42 235.27 325.49 15.7 11.6 FEP 1 0.00 119.271.10 0.1 — — — — — — FEP 1 0.00 117.13 −1.04 0.1 — — — — — — FEP 1 0.00117.47 −0.70 0.1 — — — — — — MFA 0 1.00 135.23 0.94 0.1 — 310.44 — 327.90.0 0.0 MFA 0 1.00 134.35 0.06 0.1 — 312.6 — 330.31 0.0 0.0 MFA 0 1.00133.30 −0.99 — — 310.44 — 327.9 0.0 0.0 MFA 0 1.00 135.23 0.94 — — 312.6— 330.31 0.0 0.0 MFA 0 1.00 134.35 0.06 — — 310.44 — 327.9 0.0 0.0 MFA 01.00 133.30 −0.99 — — 312.6 — 330.31 0.0 0.0 MFA 0.1 0.90 133.68 0.560.1 — 310 — 327.65 0.0 0.0 MFA 0.1 0.90 133.90 0.78 — — 310 — 327.65 — —MFA 0.1 0.90 132.55 −0.57 — — 310 — 327.65 — — MFA 0.15 0.85 133.58 1.040.1 — 309.65 — 327.77 0.0 0.0 MFA 0.15 0.85 133.46 0.92 — — 309.65 —327.77 — — MFA 0.15 0.85 133.73 1.19 — — 309.65 — 327.77 — — MFA 0.250.75 131.09 −0.28 0.1 — 311.07 — 326.32 0.0 0.0 MFA 0.25 0.75 129.69−1.68 — — 311.07 — 326.32 — — MFA 0.25 0.75 129.86 −1.51 — — 311.07 —326.32 — — MFA 0.35 0.65 126.60 −3.60 0.1 287.84 307.87 — 326.25 1.8 0.0MFA 0.35 0.65 120.23 −9.97 — 287.84 307.87 — 326.25 — — MFA 0.35 0.65132.28 2.08 — 287.84 307.87 — 326.25 — — MFA 0.4 0.60 132.30 2.69 0.1283.08 306.95 — 326.1 2.3 0.0 MFA 0.4 0.60 132.42 2.81 — 283.08 306.95 —326.1 — — MFA 0.4 0.60 131.88 2.27 — 283.08 306.95 — 326.1 — — MFA 0.450.55 133.25 4.22 0.1 283.72 306.29 — 325.59 2.9 0.0 MFA 0.45 0.55 132.623.59 — 283.72 306.29 — 325.59 — — MFA 0.45 0.55 131.42 2.39 — 283.72306.29 — 325.59 — — MFA 0.5 0.50 134.16 5.72 0.1 283.55 304.71 — 325.843.1 0.0 MFA 0.5 0.50 132.86 4.42 — 283.55 304.71 — 325.84 — — MFA 0.50.50 132.06 3.62 — 283.55 304.71 — 325.84 — — MFA 0.55 0.45 132.34 4.480.1 284.7 304.18 303.13 324.71 5.1 1.6 MFA 0.55 0.45 130.89 3.03 — 284.7304.18 303.13 324.71 — — MFA 0.55 0.45 130.30 2.44 — 284.7 304.18 303.13324.71 — — MFA 0.6 0.40 132.26 4.98 0.9 285.13 302.96 303.63 323.41 4.82.1 MFA 0.6 0.40 131.84 4.56 — 285.13 302.96 303.63 323.41 — — MFA 0.60.40 132.10 4.82 — 285.13 302.96 303.63 323.41 — — MFA 0.65 0.35 131.094.40 0.7 284.76 300.23 303.36 321.93 4.6 3.0 MFA 0.65 0.35 129.69 3.00 —284.76 300.23 303.36 321.93 — — MFA 0.65 0.35 129.86 3.17 — 284.76300.23 303.36 321.93 — — MFA 0.7 0.30 131.07 4.96 0.6 285.2 301.59303.37 322.86 4.6 2.9 MFA 0.7 0.30 131.17 5.06 — 285.2 301.59 303.37322.86 — — MFA 0.7 0.30 130.18 4.07 — 285.2 301.59 303.37 322.86 — — MFA0.75 0.25 128.37 2.85 0.2 284.71 298.63 302.56 320.72 3.5 2.7 MFA 0.750.25 129.31 3.79 — 284.71 298.63 302.56 320.72 — — MFA 0.75 0.25 128.733.21 — 284.71 298.63 302.56 320.72 — — MFA 0.8 0.20 128.11 3.17 0.1284.46 296.79 301.81 319.14 2.6 2.9 MFA 0.8 0.20 127.35 2.41 — 284.46296.79 301.81 319.14 — — MFA 0.8 0.20 128.05 3.11 — 284.46 296.79 301.81319.14 — — MFA 0.9 0.10 121.91 −1.86 0.1 — 288.35 — 313.77 0.0 0.0 MFA0.9 0.10 123.99 0.22 — — 288.35 — 313.77 — — MFA 0.9 0.10 124.99 1.22 —— 288.35 — 313.77 — — MFA 1 0.00 122.94 0.34 0.1 279.88 — 304.13 — 21.913.8 MFA 1 0.00 122.50 −0.10 0.1 281.71 — 305.09 — 16.1 13.8 MFA 1 0.00122.36 −0.24 — 279.88 — 304.13 — — — PFA 0 1.00 133.30 −0.99 0.1 —310.39 — 327.85 0.0 0.0 (A) PFA 0 1.00 134.35 0.06 — — — — — 0.0 0.0 (A)PFA 0 1.00 135.23 0.94 — — — — — 0.0 0.0 (A) PFA 0.1 0.90 134.75 1.230.1 — 310.09 — 327.87 0.0 0.0 (A) PFA 0.1 0.90 135.72 2.20 0.1 — 310.09— 327.87 0.0 0.0 (A) PFA 0.1 0.90 136.08 2.56 0.1 — 310.09 — 327.87 0.00.0 (A) PFA 0.2 0.80 134.95 2.20 0.1 — 309 — 327.88 0.0 0.0 (A) PFA 0.20.80 135.12 2.37 0.1 — 309 — 327.88 0.0 0.0 (A) PFA 0.2 0.80 135.28 2.530.1 — 309 — 327.88 0.0 0.0 (A) PFA 0.4 0.60 137.00 5.79 0.7 — 306.95 —326.42 0.0 0.0 (A) PFA 0.4 0.60 138.20 6.99 0.7 — 306.95 — 326.42 0.00.0 (A) PFA 0.4 0.60 138.71 7.50 0.7 — 306.95 — 326.42 0.0 0.0 (A) PFA0.45 0.55 136.84 6.01 1 285 306.08 — 325.87 0.0 0.0 (A) PFA 0.45 0.55137.54 6.71 1 285 306.08 — 325.87 0.0 0.0 (A) PFA 0.45 0.55 137.92 7.091 285 306.08 — 325.87 0.0 0.0 (A) PFA 0.5 0.50 135.94 5.50 1 285.44305.65 300.41 324.91 4.8 4.9 (A) PFA 0.5 0.50 136.53 6.09 1 285.44305.65 300.41 324.91 4.8 4.9 (A) PFA 0.5 0.50 137.18 6.74 1 285.44305.65 300.41 324.91 4.8 4.9 (A) PFA 0.55 0.45 135.86 5.81 1 285.1304.39 302.67 324.51 5.1 37.9 (A) PFA 0.55 0.45 137.23 7.18 1 285.1304.39 302.67 324.51 5.1 37.9 (A) PFA 0.55 0.45 138.05 8.00 1 285.1304.39 302.67 324.51 5.1 37.9 (A) PFA 0.6 0.40 136.06 6.39 1 285 303.94298.43 323.23 4.0 5.6 (A) PFA 0.6 0.40 135.44 5.77 1 285 303.94 298.43323.23 4.0 5.6 (A) PFA 0.6 0.40 135.35 5.68 1 285 303.94 298.43 323.234.0 5.6 (A) PFA 0.75 0.25 132.46 3.95 0.7 285.3 300.85 295.17 320.5611.7 4.3 (A) PFA 0.75 0.25 129.88 1.37 0.7 285.3 300.85 295.17 320.5611.7 4.3 (A) PFA 0.75 0.25 132.65 4.14 0.7 285.3 300.85 295.17 320.5611.7 4.3 (A) PFA 0.9 0.10 128.07 0.71 0.1 296.12 — 296.86 316.14 33.345.0 (A) PFA 0.9 0.10 127.86 0.50 0.1 296.12 — 296.86 316.14 33.3 45.0(A) PFA 0.9 0.10 127.60 0.24 0.1 296.12 — 296.86 316.14 33.3 45.0 (A)PFA 1 0.00 126.50 −0.09 0.1 291.94 — 311.87 — 28.3 0.0 (A) PFA 1 0.00126.47 −0.12 0.1 291.94 — 311.87 — 28.3 0.0 (A) PFA 1 0.00 126.79 0.200.1 291.94 — 311.87 — 28.3 0.0 (A) PFA 0 1.00 135.23 0.94 0.1 — 310.44 —327.9 0.0 0.0 (B) PFA 0 1.00 134.35 0.06 0.1 — 310.44 — 327.9 0.0 0.0(B) PFA 0 1.00 133.30 −0.99 0.1 — 310.44 — 327.9 0.0 0.0 (B) PFA 0.150.85 128.77 −3.83 0.1 — 308.79 — 327.12 0.0 0.0 (B) PFA 0.15 0.85 126.77−5.83 0.1 — 308.79 — 327.12 0.0 0.0 (B) PFA 0.15 0.85 133.12 0.52 0.1 —308.79 — 327.12 0.0 0.0 (B) PFA 0.2 0.80 131.67 −0.37 0.1 — 307.97 —325.1 0.0 0.0 (B) PFA 0.2 0.80 131.92 −0.12 0.1 — 307.97 — 325.1 0.0 0.0(B) PFA 0.2 0.80 131.95 −0.09 0.1 — 307.97 — 325.1 0.0 0.0 (B) PFA 0.30.70 129.38 −1.53 0.3 — 306.33 — 326.42 0.0 0.0 (B) PFA 0.3 0.70 132.771.86 0.1 — 306.33 — 326.42 0.0 0.0 (B) PFA 0.3 0.70 131.14 0.23 0.1 —306.33 — 326.42 0.0 0.0 (B) PFA 0.4 0.60 134.42 4.63 0.7 284.33 304.38302.08 325.14 0.0 0.0 (B) PFA 0.4 0.60 133.52 3.73 0.7 284.33 304.38302.08 325.14 0.0 0.0 (B) PFA 0.4 0.60 133.69 3.90 0.7 284.33 304.38302.08 325.14 0.0 0.0 (B) PFA 0.45 0.55 135.39 6.17 0.1 — 304.02 —324.48 0.0 0.0 (B) PFA 0.45 0.55 135.26 6.04 0.1 — 304.02 — 324.48 0.00.0 (B) PFA 0.45 0.55 135.39 6.17 0.1 — 304.02 — 324.48 0.0 0.0 (B) PFA0.5 0.50 135.78 7.12 0.9 281.64 302.69 — 323.34 2.0 0.0 (B) PFA 0.5 0.50134.98 6.32 0.9 281.64 302.69 — 323.34 2.0 0.0 (B) PFA 0.5 0.50 135.276.61 0.9 281.64 302.69 — 323.34 2.0 0.0 (B) PFA 0.55 0.45 133.84 5.740.9 281.16 301.88 — 316.5 2.2 0.0 (B) PFA 0.55 0.45 135.15 7.05 0.9281.16 301.88 — 316.5 2.2 0.0 (B) PFA 0.55 0.45 133.91 5.81 0.9 281.16301.88 — 316.5 2.2 0.0 (B) PFA 0.6 0.40 130.12 2.59 0.5 281.75 300.23 —321.15 1.3 0.0 (B) PFA 0.6 0.40 131.32 3.79 0.5 281.75 300.23 — 321.151.3 0.0 (B) PFA 0.6 0.40 131.65 4.12 0.5 281.75 300.23 — 321.15 1.3 0.0(B) PFA 0.7 0.30 131.27 4.86 0.8 252.07 297.29 — 319.71 0.0 0.0 (B) PFA0.7 0.30 131.32 4.91 0.8 252.07 297.29 — 319.71 0.0 0.0 (B) PFA 0.7 0.30130.62 4.21 0.8 252.07 297.29 — 319.71 0.0 0.0 (B) PFA 0.75 0.25 127.701.86 0.5 254.53 296.54 — 318.33 0.0 0.0 (B) PFA 0.75 0.25 129.14 3.300.1 254.53 296.54 — 318.33 0.0 0.0 (B) PFA 0.75 0.25 128.03 2.19 0.1254.53 296.54 — 318.33 0.0 0.0 (B) PFA 0.8 0.20 127.99 2.71 0.4 249.05291.86 — 315.78 0.6 0.0 (B) PFA 0.8 0.20 126.40 1.12 0.4 249.05 291.86 —315.78 0.6 0.0 (B) PFA 0.8 0.20 127.51 2.23 0.4 249.05 291.86 — 315.780.6 0.0 (B) PFA 0.9 0.10 126.29 2.14 0.5 251.12 292.45 294.28 314.19 0.00.0 (B) PFA 0.9 0.10 126.41 2.26 0.5 251.12 292.45 294.28 314.19 0.0 0.0(B) PFA 0.9 0.10 126.27 2.12 0.5 251.12 292.45 294.28 314.19 0.0 0.0 (B)PFA 1 0.00 122.83 −0.20 0.1 308.79 308.79 309.18 309.18 58.2 14.6 (B)PFA 1 0.00 122.93 −0.10 0.1 308.79 308.79 309.18 309.18 58.2 14.6 (B)PFA 1 0.00 123.32 0.29 0.1 308.79 308.79 309.18 309.18 58.2 14.6 (B)

Example 8 PFA/LPTFE Blends

Example 8 is an extension of previous Examples for further measurementsmade on PFA/LPTFE blends. In this Example, two systems were examinedbased on TE-7224 (PFA (B)) and PFA6900Z (PFA (A)), respectively.

FIG. 41 shows the normalized heat of fusion for these polymer blends asa function of [MPF], a peak is visible in both cases centered on aweight fraction MPF=ca 0.53. Likewise FIGS. 42 and 43 show peaks in thecontact angle data at the same concentration. FIG. 43 plots thedifference between the observed contact angle and that expected from alinear interpolation between the two components; there is a greater than6 degree difference at the optimal concentration of [MPF]=0.53 withsignificant differences between [MPF]=0.3-0.7. This behavior isprecisely mirrored in FIG. 44, which shows the acid resistance after 6hours exposure to HCL. Under these conditions, both pure components havefailed catastrophically. However, the compositions in the region of[MPF]=ca 0.53 remain pristine.

FIGS. 45 and 46 show the melting points of the PFA based samples andgive some indication of local maxima associated with the optimalcompositions discussed above. Finally, FIG. 47 shows the acid resistanceperformance with time and [MPF] in a contour plot; the darker regionsrepresent superior performance, it is quite clear from this figure thatprolonged acid resistance is only obtainable at compositions between[MPF]=ca 0.3-0.75.

Example 9 FEP/LPTFE Blends

Example 9 is an extension of previous Examples for further measurementsmade on FEP/LPTFE blends in this case a different system was examinedbased on ND-110.

FIG. 48 shows the normalized heat of fusion for this polymer blend as afunction of [MPF], a peak is visible in this case centered on a weightfraction, MPF=0.5. Likewise, FIGS. 49 and 50 show peaks in the contactangle data at the same concentration, but an additional peak is alsoobserved at [MPF]=ca 0.7. FIG. 50 plots the difference between theobserved contact angle and that expected from a linear interpolationbetween the two components; there is a greater than 3 degree differenceat these optimal concentrations of [MPF]=ca 0.5-0.7, with significantdifferences between [MPF]=0.4-0.8. This behavior is precisely mirroredin FIG. 51, which shows the acid resistance after 6 hours exposure toHCL. Under these conditions, both pure components have failedcatastrophically. However, the compositions in the region of [MPF]=ca0.35-0.6 remain pristine and there is some indication that at [MPF]=0.7acid resistance is slightly enhanced.

FIGS. 52 and 53 show the melting points of the FEP based samples andgive some indication of local maxima associated with the optimalcompositions discussed above.

Finally, FIG. 54 shows the acid resistance performance with time and[MPF] in a contour plot; the darker regions represent superiorperformance, it is quite clear from this figure that prolonged acidresistance is only obtainable at compositions between [MPF]=0.3-0.6,with samples outside this range failing quickly.

Example 10 MFA/LPTFE Blends

Example 10 is an extension of previous Examples for further measurementsmade on MFA/LPTFE blends.

FIG. 55 shows the normalized heat of fusion for this polymer blend as afunction of [MPF], a peak is visible in this case centered on a weightfraction, MPF=ca. 0.65. Likewise, FIGS. 56 and 57 show peaks in thecontact angle data at the same concentration. FIG. 57 plots thedifference between the observed contact angle and that expected from alinear interpolation between the two components; there is a greater than5 degree difference at the optimal concentration of between [MPF]=ca0.45-0.7 with significant differences between [MPF]=0.45-0.8. Thisbehavior is mirrored in FIG. 58, which shows the acid resistance after 6hours exposure to HCL. Under these conditions, both pure components havefailed catastrophically. However, the compositions in the region of[MPF]=ca 0.6-0.7 are largely unaffected.

FIGS. 59 and 60 show the melting points of the MFA based samples andgive some indication of local maxima associated with the optimalcompositions discussed above.

Finally, FIG. 61 shows the acid resistance performance with time and[MPF] in a contour plot; the darker regions represent superiorperformance, it is quite clear from this figure that prolonged acidresistance is only obtainable at compositions between [MPF]=ca0.55-0.75, with samples outside this range failing quickly.

Example 11 PFA/LPTFE Blend Using DuPont TE-7224/TE-3887N

Blends of PFA TE-7224 with DuPont's Zonyl TE-3887N LPTFE were made in ananalogous manner to those of Example 10 given above with the SFN-D beingsubstituted by TE-3887N. Measurement of the heat of fusion data for thePFA component (FIG. 62) showed very similar behavior as for Example 3(FIG. 41) indicating that this substitution had a negligible effect. Wemeasure the first melting point of SFN-D as 327.9 deg C. and that ofTE-3887N as 329.9 deg C. indicating that TE-3887N is higher in mwt thanSFN-D and that such a change in mwt has a negligible impact on optimumblend properties. FIGS. 63 and 64 show the contact angle and contactangle difference respectively for these TE-7224/TE-3887 blends and hereagain a peak in the data at approximately MPF=0.5 is observed consistentwith the heat of fusion data and the analogous plots of Example 10i.e.FIGS. 42 and 43, further demonstrating the negligible impact of the useof a different LPTFE.

While this invention has been described as having a preferred design,the present invention can be further modified within the spirit andscope of this disclosure. This application is therefore intended tocover any variations, uses, or adaptations of the invention using itsgeneral principles. Further, this application is intended to cover suchdepartures from the present disclosure as come within known or customarypractice in the art to which this invention pertains and which fallwithin the limits of the appended claims.

What is claimed is:
 1. A blended fluoropolymer dispersion, comprising: polytetrafluoroethylene (PTFE) having a first melt temperature (T_(m)) of 332° C. or less, in the form of a liquid dispersion of particles having a mean particle size of 1.0 microns (μm) or less; and a melt processible fluoropolymer (MPF) in the form of a liquid dispersion of particles having a mean particle size of 1.0 microns (μm) or less.
 2. The blended fluoropolymer composition of claim 1, wherein said polytetrafluoroethylene (PTFE) dispersion has a mean particle size selected from the group consisting of 0.9 microns (μm) or less, 0.75 microns (μm) or less, 0.5 microns (μm) or less, 0.4 microns (μm) or less, 0.3 microns (μm) or less, and 0.2 microns (μm) or less.
 3. The blended fluoropolymer composition of claim 1, wherein said polytetrafluoroethylene (PTFE) has a first melt temperature (T_(m)) selected from the group consisting of 330° C. or less, 329° C. or less, 328° C. or less, 327° C. or less, 326° C. or less, and 325° C. or less.
 4. The blended fluoropolymer composition of claim 1, wherein said polytetrafluoroethylene (PTFE) dispersion is obtained via emulsion polymerization and without being subjected to agglomeration, thermal degradation, or irradiation.
 5. The blended fluoropolymer composition of claim 1, wherein said polytetrafluoroethylene (PTFE) dispersion includes less than 1.0 wt. % surfactant, based on the weight of said polytetrafluoroethylene (PTFE) dispersion.
 6. The blended fluoropolymer composition of claim 1, wherein said melt processible fluoropolymer (MPF) is selected from the group consisting of perfluoroalkyl vinyl ethers and fluorinated ethylene propylene.
 7. The blended fluoropolymer composition of claim 1, wherein said melt processible fluoropolymer (MPF) has a melt flow rate (MFR) of at least 4.0 g/10 min.
 8. The blended fluoropolymer composition of claim 1, wherein said melt processible fluoropolymer (MPF) is perfluoropropylvinvyl ether (PFA), said composition having a PFA content of 37 wt. % to 80 wt. % and a PTFE content of 20 wt. % to 63 wt. %, based on the total solids of said PTFE and PFA.
 9. The blended fluoropolymer composition of claim 1, wherein said melt processible fluoropolymer (MPF) is perfluoropropylvinvyl ether (PFA), said composition having a PFA content of 37 wt. % to 65 wt. % and a PTFE content of 35 wt. % to 63 wt. %, based on the total solids of said PTFE and PFA.
 10. The blended fluoropolymer composition of claim 1, wherein said melt processible fluoropolymer (MPF) is perfluoropropylvinvyl ether (PFA), said composition having a PFA content of 43 wt. % to 63 wt. % and a PTFE content of 37 wt. % to 57 wt. %, based on the total solids of said PTFE and PFA.
 11. The blended fluoropolymer composition of claim 1, wherein said melt processible fluoropolymer (MPF) is perfluoropropylvinvyl ether (PFA), said composition having a PFA content of 50 wt. % to 60 wt. % and a PTFE content of 40 wt. % to 50 wt. %, based on the total solids of said PTFE and PFA.
 12. The blended fluoropolymer composition of claim 1, wherein said melt processible fluoropolymer (MPF) is perfluoromethylvinvyl ether (MFA), said composition having a MFA content of 35 wt. % to 90 wt. % and a PTFE content of 10 wt. % to 65 wt. %, based on the total solids of said PTFE and MFA.
 13. The blended fluoropolymer composition of claim 1, wherein said melt processible fluoropolymer (MPF) is perfluoromethylvinvyl ether (MFA), said composition having a MFA content of 45 wt. % to 76 wt. % and a PTFE content of 24 wt. % to 65 wt. %, based on the total solids of said PTFE and MFA.
 14. The blended fluoropolymer composition of claim 1, wherein said melt processible fluoropolymer (MPF) is perfluoromethylvinvyl ether (MFA), said composition having a MFA content of 56 wt. % to 76 wt. % and a PTFE content of 24 wt. % to 44 wt. %, based on the total solids of said PTFE and MFA.
 15. The blended fluoropolymer composition of claim 1, wherein said melt processible fluoropolymer (MPF) is perfluoromethylvinvyl ether (MFA), said composition having a MFA content of 63 wt. % to 70 wt. % and a PTFE content of 30 wt. % to 37 wt. %, based on the total solids of said PTFE and MFA.
 16. The blended fluoropolymer composition of claim 1, wherein said melt processible fluoropolymer (MPF) is fluorinated ethylene propylene (FEP), said composition having a FEP content of 25 wt. % to 90 wt. % and a PTFE content of 10 wt. % to 75 wt. %, based on the total solids of said PTFE and FEP.
 17. The blended fluoropolymer composition of claim 1, wherein said melt processible fluoropolymer (MPF) is fluorinated ethylene propylene (FEP), said composition having a FEP content of 35 wt. % to 90 wt. % and a PTFE content of 10 wt. % to 65 wt. %, based on the total solids of said PTFE and FEP.
 18. The blended fluoropolymer composition of claim 1, wherein said melt processible fluoropolymer (MPF) is fluorinated ethylene propylene (FEP), said composition having one of a FEP content of 35 wt. % to 55 wt. % and a PTFE content of 45 wt. % to 65 wt. % and a FEP content of 60 wt. % to 90 wt. % and a PTFE content of 10 wt. % to 40 wt. %, based on the total solids of said PTFE and FEP.
 19. The blended fluoropolymer composition of claim 1, wherein said melt processible fluoropolymer (MPF) is fluorinated ethylene propylene (FEP), said composition having one of a FEP content of 40 wt. % to 50 wt. % and a PTFE content of 50 wt. % to 60 wt. % and a FEP content of 75 wt. % to 85 wt. % and a PTFE content of 15 wt. % to 25 wt. %, based on the total solids of said PTFE and FEP.
 20. A method of forming a blended fluoropolymer dispersion, comprising the step of mixing the components of claim
 1. 21. A fluoropolymer powder, obtained from the blended fluoropolymer composition of claim
 1. 22. A method of forming a fluoropolymer powder, comprising the step of drying the blended fluoropolymer composition of claim
 1. 23. A method of forming a fluorpolymer powder, comprising the step of freeze drying the blended fluoropolymer composition of claim
 1. 24. A method of coating a substrate, comprising: applying the blended fluoropolymer composition of claim 1 to the substrate; and heat curing the blended fluoropolymer composition.
 25. A method of forming a blended fluoropolymer composition, comprising the steps of: providing a first liquid dispersion of polytetrafluoroethylene (PTFE) particles having a first melt temperature (T_(m)) of 332° C. or less and a mean particle size of 1.0 microns or less; providing a second liquid dispersion of particles of a melt processible fluoropolymer (MPF) having a mean particle size of 1.0 microns or less; and mixing the first and second dispersions together.
 26. The method of claim 25, further comprising the additional step of: drying the blended fluoropolymer composition to form a powder.
 27. The method of claim 26, wherein said drying step comprises freeze drying.
 28. The method of claim 25, further comprising the additional step of: applying the blended fluoropolymer composition to a substrate; and heat curing the blended fluoropolymer composition. 